SEPARATING THE EFFECTS OF LOW-TEMPERATURE, RIPENING, AND LIGHT ON LOSS OF SCALD SUSCEPTIBILITY IN APPLES BEFORE HARVEST

'Cortland' and 'Delicious' apples (Malus domestica Borkh.) were exposed to an increasing number of hours below 10C before sequential harvests in each of 3 years. In separate experiments, 'Cortland' apples were a) sprayed with ethephon to induce ripening at moderate temperatures and b) bagged in late August to produce ripening at low light intensities. Scald development was determined after 4 to 5 months of storage at 0C. Significant negative relationships with scald development occurred for hours below 10C, harvest date, and ripening indexes at harvest; however, the regressions with percentage scald were stronger for hours below 10C than for either harvest date or ripening. When ethephon-induced ripening occurred in the absence of low temperature, scald development decreased only slightly. Bagging fruit significantly delayed the loss of scald susceptibility with increasing hours below 10C. We conclude that low temperature was most responsible for rapid, substantial loss of scald susceptibility, and that light and ripening were secondary factors in this loss, interacting with the effects of temperature. Chemical name used: (2-chloroethyl)phosphonic acid (ethephon).